The present invention relates to a speedometer for a vehicle for indicating a vehicle speed and a travelling distance that are computed on the basis of vehicle speed pulse signals outputted from a vehicle speed sensor.
Conventionally, a speedometer installed at a passenger car or the like indicates a vehicle speed and a travelling distance by utilizing vehicle speed pulse signals outputted from a vehicle speed sensor mounted at a propeller shaft or the like which connects both a transmission and a differential gear.
As to the vehicle speed pulse signal, the number of outputted pulses per a rotation of a wheel is established, and a travelling distance per a pulse is also previously established on the assumption that the tire attached to a vehicle is standard. Namely, the travelling distance can be determined by counting the number of pulses of the vehicle speed pulse signal and by multiplying the counted value by the travelling distance per a pulse. Further, a vehicle speed can be determined by determining a travelling distance per unit time.
However, when a tire is worn or when a tire size is changed, in some cases, the travelling distance previously established per a pulse and the actual travelling distance per a pulse do not correspond to each other. Further, when vehicles are of the same car family, in some cases, tire sizes thereof are different from one another in accordance with their grades. Accordingly, even when the same, in some cases, travelling distances per a pulse thereof are different from one another, depending on their grades. Therefore, a computed vehicle speed or a computed travelling distance may cause an error.
In recent years, due to the increasing demand for the control of automobiles, for example, there have been proposed various systems using speed information such as an AHS (Automated Highway System) for performing an automatic drive. In a system utilizing such speed information, there is highly demanded for the greater accuracy of speed information or travelling distance.
In view of the aforementioned facts, an object of the present invention is to provide a speedometer for a vehicle capable of indicating a highly accurate speed or a highly accurate travelling distance and of providing highly accurate speed information to a system utilizing the speed information.
In order to accomplish the above-described object, a speedometer for a vehicle according to claim 1 of the present invention comprises: first storage means for storing travelling distance data per unit pulse of a vehicle speed pulse signal outputted from a vehicle speed sensor, correction means for correcting the travelling distance per unit pulse outputted from the vehicle speed sensor; second storage means for storing the corrected travelling distance data per unit pulse inputted from the correction means; and computation means for computing at least one of a vehicle speed and a travelling distance on the basis of the travelling distance data per unit pulse stored in the first storage means when the corrected travelling distance data per unit pulse is not stored in the second storage means, and for computing at least one of the vehicle speed and the travelling distance on the basis of the corrected travelling distance data per unit pulse when the corrected travelling distance data per unit pulse is stored in the second storage means.
In accordance with claim 1 of the present invention, travelling distance data per unit pulse of a vehicle speed pulse signal outputted from a vehicle speed sensor is stored. The second storage means stores the corrected travelling distance data per unit pulse (corrected data) inputted from the correction means, preferably, the navigation device, for correcting a travelling distance per unit pulse of a travelling speed pulse signal outputted from the vehicle speed sensor.
The navigation device is able to detect the position of a vehicle on the basis of GPS signals from a plurality of GPS satellites disposed in the space at an altitude of about 20,000 km (a so-called GPS navigation method). Further, in some cases, since the GPS signal includes an error, the navigation device receives a DGPS (Differential GPS) signal that contains correction information for correcting the vehicle position detected by the GPS signal as needed, thus correcting the vehicle position by the received correction information. Moreover, in the case of a navigation device capable of displaying thereon the calculated vehicle position so as to superimpose the same on a map, the vehicle position can be calculated more highly accurately by making use of a so-called map matching in which a road on which the vehicle is travelling is predicted and the vehicle position is matched onto the road.
Due to the vehicle pulse signal outputted from a vehicle speed sensor and the travelling direction data outputted from a gyro sensor, the navigation device can carry out a so-called independent navigation method. The independent navigation method and the GPS navigation method can be used in combination with each other to thereby calculate the vehicle position more highly accurately. Such a navigation device has a function of highly accurately correcting a travelling distance per unit pulse of a vehicle speed pulse signal outputted from the vehicle speed sensor. Further, a so-called xe2x80x9clearningxe2x80x9d is carried out to further improve the accuracy in correcting a travelling distance per unit pulse.
The computation means computes at least one of a vehicle speed and a travelling distance on the basis of travelling distance data per unit pulse that is stored in the first storage means when the corrected data is not stored in the second storage means, and the computing means computes at least one of the vehicle speed and the travelling distance on the basis of the corrected data stored in the second storage means when the corrected data is stored in the second storage means.
A travelling distance can be determined by counting the number of pulses of a vehicle speed pulse signal and by multiplying this counted value by the traveling distance data per unit pulse or the corrected data. A vehicle speed can be determined from a traveling distance data per unit time.
Thus, since the corrected data, i.e., the corrected travelling distance per unit pulse is utilized to determine a vehicle speed and a travelling distance, even when a tire is worn or even when a tire size is changed, the vehicle speed and the travelling distance are corrected highly accurately. Further, for example, in the case in which the power is not supplied to the navigation system, or in the case in which it takes a long time to rise the navigation device immediately after the power is supplied, and the like, the corrected data prestored in the second storage means, namely, the corrected travelling distance data per unit pulse can be used to compute a vehicle speed and a travelling distance. Consequently, the vehicle speed and the travelling distance can be computed highly accurately.
Claim 2 is the speedometer for a vehicle according to claim 1 of the present invention, further comprising outputting means for outputting a vehicle speed that is computed by the computation means to a speed information service system.
In accordance with claim 2 of the present invention, since the speedometer for a vehicle further comprises the outputting means for outputting a vehicle speed that is computed by the computation means to a speed information service system, the corrected vehicle speed is outputted to a system using speed information such as an AHS or the like to thereby carry out a highly accurate control.